The present invention relates to a decorative sheet for use, for example, in building interior materials, such as walls, and surface materials of, for example, fittings, such as doors, and furniture, and a decorative material comprising the decorative sheet laminated onto a substrate. More particularly, the present invention relates to a decorative sheet which is good in surface properties, such as abrasion resistance, as well as in processability and, when laminated onto a substrate as an adherend (an adherend substrate), is less likely to be broken, and a decorative material comprising the decorative sheet laminated onto the adherend substrate.
In general, surface properties, such as abrasion resistance and stain resistance, have hitherto been required of decorative sheets used in the above applications. In order to cope with this, for example, Japanese Patent Publication No. 31033/1974 discloses a decorative sheet which has been produced by printing a pattern layer on a paper substrate, coating an unsaturated polyester prepolymer (an ionizing radiation-curable resin) coating composition onto the surface of the printed substrate to form a coating, and then applying an electron beam to the coating to cause crosslinking and curing of the coating, thereby forming a surface resin layer as a surface layer.
When the surface resin layer, which has been formed by crosslinking and curing an ionizing radiation-curable resin comprising a monomer, a prepolymer or the like by applying an ionizing radiation, such as an electron beam, is provided as a surface layer constituting the outermost surface of a decorative sheet, the high degree of crosslinking can provide a decorative sheet possessing excellent surface properties such as excellent abrasion resistance and stain resistance.
In the above decorative sheet, however, upon the application of an ionizing radiation for crosslinking the surface resin layer, the cellulose molecule of the pulp in the paper substrate is broken, and a carboxyl group or a carbonyl group is produced at the cut end. As a result, the strength of the paper substrate is deteriorated, and the processability of the decorative sheet is disadvantageously lowered. More specifically, when a decorative sheet is press-laminated by means of a roller, for example, onto an adherend substrate, such as a plywood while interposing an adhesive between the decorative sheet and the adherend substrate, the decorative sheet is sometimes broken, for example, due to an increase in tension applied to the decorative sheet and mechanical vibration. In particular, when a decorative sheet is applied, for example, by lapping, onto an adherend substrate in its curved surface or a prismatic adherend substrate in its corner portion, a local stress concentration takes place in the decorative sheet. Therefore, the decorative sheet is likely to break.
In view of the above problems, it is an object of the present invention to improve the processability of a decorative sheet comprising a paper substrate bearing a surface resin layer formed of a crosslinked product of an ionizing radiation-curable resin, for improving surface properties such as abrasion resistance, and to provide a decorative material with this decorative sheet being laminated thereonto.
According to the present invention, there is provided a decorative sheet comprising a stack of:
(1) a surface resin layer formed of a crosslinked product of an ionizing radiation-curable resin; and
(2) a combinational layer comprising a combination of a paper substrate and a high-modulus resin having a tensile strength of not less than 40 MPa as measured according to JIS K 6301.
Further, according to the present invention, there is provided a decorative material comprising the above decorative sheet laminated onto an adherend substrate.
In this way, by virtue of the combination of a paper substrate with a high-modulus resin, the strength of the whole decorative sheet can be maintained even when the strength of the paper substrate is deteriorated due to the cleavage of the cellulose molecule of the pulp in the paper substrate upon the application of an ionizing radiation at the time of the formation of the surface resin layer. This can realize a decorative sheet which possesses surface properties such as abrasion resistance exerted by the surface resin layer and, at the same time, possesses good processability. Therefore, in laminating the decorative sheet onto an adherend substrate, for example, by means of a roll laminator, it is possible to prevent the decorative sheet from being broken, for example, due to mechanical vibration or a shock caused in the case where the carrying of a decorative sheet in a continuous strip form, every time when applied onto an adherend substrate (in a sheet form), is stopped to cut the decorative sheet, specifically an instantaneous increase in tension.
The high-modulus resin is preferably combined with the paper substrate by a method wherein the high-modulus resin layer is formed on the surface of the paper substrate, or by impregnating the high-modulus resin into the paper substrate. When the high-modulus resin layer is formed on the surface of the paper substrate, the high-modulus resin layer may be formed on the top surface side of the paper substrate, that is, on the paper substrate in its surface resin layer side, or alternatively may be formed on the backside of the paper substrate, that is, on the paper substrate in its side remote from the surface resin layer. On the other hand, in the impregnation of the high-modulus resin into the paper substrate, the high-modulus resin may be impregnated into the paper substrate in its top surface side or back surface side, or alternatively may be impregnated into the whole paper substrate.
Preferably, in the decorative sheet having the above construction according to the present invention, the paper substrate is formed of a needle-leaved tree pulp. As compared with the use of the broad-leaved tree pulp, the use of the needle-leaved tree pulp in the paper substrate can increase the strength of the paper substrate, and, thus, even when the strength is deteriorated by the application of an ionizing radiation, the strength of the decorative sheet can be further improved.
Further, in any one of the above constructions of the decorative sheet according to the present invention, preferably, the paper substrate comprises a pulp which has at least one of carboxyl and carbonyl groups at a cut end formed as a result of the cleavage of a cellulose molecule.
According to the present invention, the use of the paper substrate formed of this pulp can maximize the effect of the high-modulus resin layer.
This decorative material possesses excellent surface properties, such as excellent abrasion resistance, and, at the same time, is less likely to cause troubles, such as sheet breaking, at the time of the application of the decorative sheet onto the adherend substrate and thus can be produced in high yield.